Grapevine is one of the only karaoke bars within a many, many mile radius. Because of this, Grapevine gets an A-OK because this bar can offer a good time if you go in the right mindset. The right mindset is when you're ready to belt it out with the "best of them" aka, a combination of elderly people and really drunk young people.
I would really only ever go to the Grapevine for karaoke. I've eaten here a couple of times and the food is par. The venue itself is older, a little warn down and in need of some TLC. However, the clientele probably doesn't case because again, most people visit the Grapevine after several cocktails in order to live out their dreams of being on America Idol.
Be warned that the while the Grapevine itself is spacious with a decently sized second floor deck, the karaoke is inside and it can get very cramped. There are only a handful of tables inside and on a night and especially a weekend night, it will be very crowded and will most likely take a little bit of time to get a drink and sing. The old timers who are regulars here take their singing very seriously so don't even think about cutting in front of them! :)